<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>单列布局</title>
</head>
<style>
    .header{
        margin:0 auto; 
        max-width: 960px;
        height:100px;
        background-color: blue;
    }
    .nav{
        margin: 0 auto;
        max-width: 800px;
        background-color: darkgray;
        height: 50px;
    }
    .content{
        margin: 0 auto;
        max-width: 960px;
        height: 400px;
        background-color: aquamarine;
    }
    .footer{
        margin: 0 auto;
        max-width: 960px;
        height: 100px;
        background-color: aqua;
    }
</style>
<body>
    <div class="header">
        <div class="nav"></div>
    </div>
    <div class="content"></div>
    <div class="footer"></div>
</body>
</html>